The present invention relates to an output control technique of controlling a laser pulse of a solid-state laser, which is excited by a semiconductor laser array, in time-function waveform.
Recently, the number of cases where a very thin material is processed using a solid-state laser (e.g., welding of an aluminum plate having a thickness of 0.1 mm or less and deposition of plastic components) has been increased as electronic components are miniaturized. Therefore, as shown in FIG. 5A, the pulse width ranges from 100 xcexcs to 500 xcexcs, and the pulse waveform of the solid-state laser has to be controlled by setting the current of one pulse as a function of time.
As a method of controlling the pulse output from a solid-state laser in arbitrary waveform, it can be thought to optically form a pulse through a Q-switching operation or under the control of a power supply.
In the Q-switching operation, a pulse is formed optically by the operation of a high-speed shutter set in an optical resonator. In other words, when the high-speed shutter is opened, a laser oscillator consumes energy accumulated in an excitation medium and starts to oscillate. The laser oscillator stops oscillating when it completely consumes the energy. The time period during which the laser oscillator oscillates corresponds to the pulse width. Usually, the pulse width is of the order of nanoseconds and the pulse is in a single-peak shape. Since the Q-switching operation is a self-excited oscillation, it is difficult to control one pulse in arbitrary form.
In the self-excited oscillation, a very-high-density inverted population is achieved if a loss of the optical resonator is increased to prevent the laser oscillator from oscillating while the laser oscillator is pumping laser materials and, if the loss is suddenly decreased to obtain a large Q value which is advantageous for oscillation, the accumulated energy is released explosively in several nanoseconds to several tens of nanoseconds. The Q-switching operation is performed based on the above principle. It is therefore difficult to control one pulse of a laser beam in arbitrary form at time resolution of 10 xcexcs to 500 xcexcs.
According to the power supply control, a pulse is excited by controlling electric energy applied to a flash lamp serving as an excitation source. Since, in this case, the power supply control is electric control, the pulse width and pulse shape can be controlled relatively easily if the pulse width is larger than a certain value. For example, Jpn. Pat. Appln. KOKAI Publication No. 4-42979 discloses a technique of controlling heat input to a process point by controlling one pulse in arbitrary waveform when the pulse width ranges from 1 ms to 20 ms.
Since, however, the start-up responsivity of the flash lamp falls within a range of 100 xcexcs to 500 xcexcs, it is extremely difficult to control one pulse in arbitrary form when the pulse width ranges from 10 xcexcs to 500 xcexcs.
FIGS. 5A to 5C are graphs of pulse waveforms controlled by the excitation of a flash lamp. FIG. 5A shows a preset waveform in which the pulse width is set to five steps which differ from each other by 20 xcexcs within 100 xcexcs. FIG. 5B shows a current waveform. However, it does not correspond to the preset waveform at all when the pulse width is 100 xcexcs but simply exhibits a single curve. FIG. 5C shows a laser waveform. Like the current waveform, the laser waveform does not correspond to the preset waveform at all when the pulse width is 100 xcexcs. There is no correlation between the laser waveform and the preset waveform when the pulse width is 100 xcexcs. The laser waveform also simply exhibits a single curve.
In other words, the flash lamp excitation requires response time of at least 100 xcexcs, so that the current and laser waveforms cannot follow the preset waveform varying 20 xcexcs by 20 xcexcs and greatly differ in shape from the preset waveform.
As the rising characteristics of pulses of the flash lamp, the flash lamp is large in individual difference and easy to vary with time. For example, when a sharp peak is set at the beginning of a pulse waveform which corresponds to the pulse width of 100 xcexcs, the peak is always susceptible to individual differences of the flash lamp and variations with time thereof, which greatly influences a process using the flash lamp.
Because of the above-described characteristics of the flash lamp, it is very difficult to control one pulse in time-function waveform when the pulse width is 500 xcexcs or less.
The object of the present invention is to achieve a high-precision laser process by controlling one pulse in time-function waveform even when the pulse width is 500 xcexcs or less.
According to the present invention, there is provided a power supply unit for a solid-state laser using a semiconductor laser array as an excitation light source, comprising a plurality of chopper circuits arranged between a direct-current power supply and an output terminal of the semiconductor laser array and connected in parallel with each other, for applying resultant power of the chopper circuits to the semiconductor laser array, and a current controller for controlling the plurality of chopper circuits to modulate the resultant power at time resolution ranging from 1 xcexcs to 100 xcexcs.
The present invention allows one pulse to be modulated and controlled in time-function waveform at time resolution ranging from 1 xcexcs to 100 xcexcs even when the pulse width is 500 xcexcs or less, with the result that a high-precision laser process can be executed.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.